A well-received window covering at the present time consists of an extent of pleated fabric which can be expanded to cover a window, for example, and also withdrawn folding upon itself along the pleat lines to leave the window unobstructed. Such window covering units for a window in a vertical wall typically have one or more cords which pass through aligned openings in the pleated fabric and can be manipulated to raise or lower a rail at one end to adjust the window covering and move it from closed to open or to any intermediate position desired.
Where the window to be adjustably covered by a window covering unit is on a vertical wall and not too far above the ground plane, access in the usual case does not pose great difficulty. However, in the case of a ceiling window or skylight, several difficulties immediately present themselves. First of all, the window covering unit is at some distance from the ground level or room floor and requires special apparatus for long range adjustment for correct operation. In addition, the window covering unit moves in a horizontal plane rather than vertically as in the case of a vertical wall window, for example, and therefore must be driven to its various adjustment positions without the aid of gravity. A still further source of possible difficulty is that the window covering unit must be carefully constructed so as not to become easily jammed and, in fact, should be substantially fool-proof in this regard. That is, whereas a window covering unit closely adjacent the floor can be easily reached for manipulative release of a jam, where it is located on the ceiling this becomes manifestly more difficult requiring step ladders or the like and presenting some danger of falling to an individual attempting repair.